Low temperature electrochemical cells and batteries



Feb. 13, 1968 M. s. TOY 3,368,926

LOW TEMPERATURE ELECTROCHEMICAL CELLS AND BATTERIES Filed April l5, 1966 2 Sheets-Sheet 1 Feb. 13, 1968 M. s. ATOY 3,368,925

LOW TEMPERATURE ELECTROCHEMICAL CELLS AND BATTERIES Filed April l5, 1966 2 Sheets-Sheet 2 Eid-3- lllllll l l l l wmm lllll ."O'L` 0.0463m l l United States Patent Oiiiice 3,368,926 Patented Feb. 13, 1968 3,368,926 LOW TEMPERATURE ELECTROCHEMICAL CELLS AND BATTERIES Madeline S. Toy, Fountain Valley, Calif., assigner, by

mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Apr. 15, 1966, Ser. No. 543,773 7 Claims. (Cl. 136-155) This invention relates to a new and improved type of electrolytic cell and has particular relation to an electrolyte solution for use therein.

In electrolytic cells or batteries intended for extreme low-temperature service, the electrolyte employed must have a eutectic point at a temperature below that anticipated in the intended service. In the relatively new field of cryogenics, experimentation concerns itself with temperatures of 60 C. and below. There are times during such experimentation when an internal power source is desirable. The ordinary dry cell becomes inoperative at about 20 C. and even recent improvements lower its operability to only 50 C. At these lower limits of temperature the electrolyte solution freezes and the internal resistance of the cell 'becomes very high.

An object of the present invention is to provide an electrolyte solution for a low-temperature electrolytic cell which will permit efficient operation from 60 C. t 132 C.

Another object of the invention is to provide an electrolyte solution which will have desirable dry cell characteristics, including solubility of the salts contained therein, freezing temperature, viscosity, resistivity, temperature coeicient, acidity and satisfactory chemical reactions with other constituents of the cell at low temperatures. These and other objects of the invention will be better understood by reference to the accompanying description and by the curves shown in FIGURES 1 to 4 of the drawings.

I have discovered that liquid nitrosyl liuoride is an excellent ionizing solvent. It has a relatively high degree of self-ionization which probably occurs in the following manner:

The advantages of nitrosyl fluoride as a solvent for electrochemical cells and batteries are: (l) its low temperature liquid range (M.P. 132 C. and B.P. 60 C.), (2) its solvation characteristics enabling it to form highly conductive electrolytic solutions (`2 ohm-1 cm.l) at temperatures below 60 C., and (3) its high eiectrochemical energy potential due to higher free energy change of fluorination reactions as compared to oxidation reactions.

Further, experimentation indicated that liquid nitrosyl fluoride is a good ionizing solvent for nonpolar Lewis acids such as boron trifluoride, phosphorus pentauoride and arsenic pentafluoride and the nitrosyl (e.g. NOBF4, NOPFG, NOAsFS) and nitryl (eg. NOzAsF, NO2SbF6) salts of such a-cids. These mixtures form highly conductive electrolytic solutions at temperatures below 60 C.

SPECIFIC CONDUCTIVITIES OF SOME NITROSYL AND NIIRYL SALTS IN LIQUID NITROSYL FLUORIDE Solute Concentration Temperature Specific Con- (mole/lter) C. ductivlty (ohm-l cmrl) 0.403 90 4. 42 10a 0. 379 -90 1. 33 102 0. 446 -90 5. 41 X10-3 1.0 1.15)(10-2 1, 0 -80 1.(3 102 Pure -80 6. 24)(10-5 Pure 3. 95 105 The effect of the addition of the nonpolar Lewis acids to nitrosyl fluoride can more easily be seen by reference to FIGURE 1 which depicts specific conductivities as a function of concentrations of BF3, PF5, and ASF;J in NOF solutions at 60 C. At that temperature the specific conductivity increases proportionately with the addition of the acid, reaching maximum conductivity at a concentration of approximately 0.286 mole per 1000 grams of NOF for PF5, 0.336 mole per 1000 grams of NOF for AsF5, and 0.304 mole per 1000 grams of NOF for BF`3. As can be further derived from FIGURE 1, at the stated maximum effective concentrations the approximate specific conductivities are 9.0 10'1 ohm*1 cm1 for PF5, 1.9 10-2 ohm-1 cm.-l for AsF5, and 3.8 102 ohm*1 cm.-1 for BF3.

FIGURE 2 illustrates the specific conductivity as a function of temperature of varying concentrations of BF3 in NOF. At a concentration of 0.304 mole BFS per 1000 grams of NOF, the specific conductivity decreases as the temperature decreases, from a high of 3.5X10-2 ohm-1 cm.1 at 60 C. It can be seen that the BF3 solution exhibits considerably greater specific conductivity than pure NOF which has a specific conductivity of 9.5 X 10-3 ohm-1 cm.-1 at 60 C.

In the same manner, FIGURE 3 describes the relationship between temperature and the specific conductivity of various concentrations of phosphorus pentafluoride in nitrosyl uoride. The most suitable concentration is 0.286 mole of PF5 per 1000 grams of NOF which, for example, has a specc conductivity of 9.3 101 ohm"1 crn1 at 80 C.

Similarly, FIGURE 4 shows AsF5 in the context of concentration, temperature and specic conductivity. The suggested concentration of arsenic pentauoride is 0.336 mole per 1000 grams of NOF. That solution has a specific conductivity of 4.0 102 ohm-1 crn.-1 at 90 C.

While only preferred forms of the invention are shown and described, other forms thereof are contemplated and numerous changes and modifications may be made therein without departing from the spirit of the invention as set forth in the appended claims.

What is claimed is:

1. A low-temperature battery having an electrolyte therein, said electrolyte comprising liquid nitrosyl fluoride.

2. The electrolyte set forth in claim 1, including at least one nonpolar Lewis acid from the group of acids consisting of phosphorus pentauoride, arsenic pentaliuoride and boron triuoride.

3. The electrolyte set forth in claim 2, wherein phosphorus pentafluoride comprises up to 0.286 mole per onethousand grams of nitrosyl uoride, arsenic pentauoride comprises up to 0.336 mole per one-thousand grams of nitrosyl iiuoride, and boron triuoride comprises up to 0.304 mole per one-thousand grams of nitrosyl fluoride.

4. The electrolyte set forth in claim 1, including at least one nitrosyl salt from the .group consisting of NOBF4, NOPF6, and NOASFS.

5. The electrolyte set forth in claim 4, wherein the concentration of said NOBF4 is 0.403 mole per liter of NOF, of NOPFG is 0.379 mole per liter of NOF, and 0f NOAsF is 0.446 mole per liter of NOF.

6. The electrolyte set forth in claim 1, including at least one nitryl salt from the group consisting of NOzAsF and NO2SbF6.

4 7. The electrolyte set forth in claim 6, wherein the concentration of NOZASFG is 1.0 mole per liter of NOF and of NO2SbF6 is 1.0 mole per liter of NOF.

References Cited UNITED STATES PATENTS 2,773,786 12/1956 Jobe 136-155 2,950,999 8/1960 Craig et al 136--155 3,320,140 5/1967 Yodis 204-59 ALLEN B. CURTIS, Primary Examiner.

D. L. WALTON, Assistant Examiner. 

1. A LOW-TEMPERATURE BATTERY HAVING AN ELECTROLYTE THEREIN, SAID ELECTROLYTE COMPRISING LIQUID NITROSYL FLUORIDE. 